Conventionally, a method and apparatus for forming a silicon nitride film, and a cleaning pre-processing method of the forming apparatus, which are capable of suppressing generation of hydrogen chloride during maintenance operations, have been known.
This forming apparatus includes a reaction tube for forming a silicon nitride film on a semiconductor wafer by supplying hexachlorodisilane and ammonia, and an exhaust pipe connected to the reaction tube. Further, before the exhaust pipe is disassembled and cleaned, the reaction tube is heated. to 500 to 900 degrees C. by a temperature rising heater, and the exhaust pipe and a valve are heated to 100 to 200 degrees C. by an exhaust pipe heater. And, ammonia, is supplied from a process gas introduction pipe. In this manner, by heating the exhaust pipe and the valve by the exhaust pipe heater, an ammonium chloride may be maintained at a vaporizable temperature and generation of a hydrogen chloride due to hydrolysis may be suppressed.
However, since properties of harmful gases generated during the maintenance are different from each other according to types of films to be formed, there may be a process that cannot suppress generation of a harmful gas even though the exhaust pipe is heated. In such a case, a method different from the foregoing method is required to suppress generation of a harmful gas.
Further, even though a harmful gas is suppressed, if substrate processing is stopped to suppress a harmful gas and a process is performed to suppress the harmful gas for a long period of time, a down time is lengthened to degrade productivity of the substrate processing.